大别山北缘深部结构的高精度重磁电震解析

大别山北缘位于大别造山带与华北陆块会聚地带,其深部精细结构还存在一些争议问题.根据近年来在研究区域内采集的地球物理数据,通过OMEGA、OASIS和FUGRO-LCT等多个重磁电震软件处理,获得了深部信息丰富的多种地球物理属性图像.本文从中选取了2条平行的电法和地震剖面,辅以高精度重磁数据,揭示了大别山北缘深部地质结构总体呈现华北陆块南向俯冲、北淮阳构造带向北逆冲的特征,并可清楚地识别大别山北缘造山带、肥南山前坳陷带和肥北斜坡带.其特征分别如下:①大别山北缘造山带,地震反射杂乱,电性高阻大于2000Ωm,以磨子潭-晓天断裂为界分为北大别杂岩带和北淮阳构造带,主要由大别群、卢镇关杂岩和佛子岭群组成,沿舒城-信阳断裂逆冲于中、下侏罗统之上,浅部发育北倾的金寨-龙门冲滑覆断裂.②肥南山前坳陷带,上部为中、新生界,呈现中低阻特征,地震反射界面清楚,断面波明显;下部为华北型前中生界沉积岩(上部可能残存古生界),电性特征为低阻(5~50 Ωm),地震反射较连续,内部反射弱.以六安断裂为界分为舒城凹陷和肥中断裂带,其北侧边界为肥中断裂.③肥北斜坡带,上部主要为侏罗系,呈现中低阻、水平层状地震反射特征;下部主要为霍邱群,电性为高阻,地震反射杂乱;中间为华北型前中生界沉积岩,向北逐渐减薄、直至缺失.上述认识将为华北陆块南向俯冲、南北板块碰撞缝合线和油气资源勘查等研究提供深部地质约束.     

深地震反射剖面揭示的海原断裂带深部几何形态与地壳形变

由于活动的青藏高原不断的隆升和推挤作用,在西南向东北的推挤作用和周缘块体的阻挡以及东北缘内部块体挤压形变的作用下,形成了多个走向不同的青藏高原东北缘构造体系.新生代构造变形和地震活动强烈,区内分布多条大型深断裂带.海原断裂是青藏高原东北缘发育的弧形活动断裂带中规模最大、活动最为强烈的一条左旋走滑型断裂带,是重要的大地构造区边界,也是控制现今强震活动的活断层.本文利用2009年完成的高分辨率深地震反射剖面的北段资料,对其进行初步构造解释,揭示出海原断裂带的深部几何形态和其两侧地壳上地幔细结构.结果显示海原断裂并不是简单的陡立或者较缓,其几何形态随着深度变化.在海原断裂之下的Moho并未错断的反射特征显示海原断裂并不是直接错断莫霍面的超壳断裂.海原断裂带及两侧岩石圈结构和构造样式的研究为探讨青藏高原东北缘岩石圈变形机制提供地震学依据.     

先验地质信息约束下的三维重磁反演建模研究 ——以安徽泥河铁矿为例

安徽泥河铁(硫)矿床是近年发现的大深度隐伏矿床,它的发现再次引发了庐枞地区深部找矿的热潮.建立矿区的三维精细地质模型,对寻找深、边部隐伏矿体,深入认识深部成矿、控矿规律意义重大.本文以泥河矿区为实例,开展先验地质信息约束的三维重磁建模研究,获得了矿区面积5.6 km²(2.8 km×2.0 km)、深度1.2 km内的三维地质模型.在三维可视化平台上对该模型进行了地质解释,全面分析了矿体、地层与次火山岩之间的空间分布及对应关系,发现铁矿主要赋存于闪长玢岩与砖桥组火山岩之间,且在玢岩穹窿地段矿体厚大,这对认识"玢岩型"铁矿的成矿模式具有重要的实际意义;三维模型的重磁正演响应基本拟合了实际重磁异常,说明在建模区域内已没有新的矿体;本文提出的三维地质建模流程可为其它地区开展类似工作提供借鉴,同时研究表明地质信息约束下的三维重磁建模研究在深、边部找矿和重磁异常的精细解剖等方面具有潜在的价值和广阔的应用前景.     

Macro- and megafauna communities in three deep basins of the South-East Atlantic

During ‘Meteor’ expedition ‘DIVA 2’ in 2005 the abyssal macro- and megafauna communities were studied in the northern Cape Basin, in the northern Angola Basin and in the eastern and western Guinea Basin. Water depths varied between 5040 and 5670 m.Surface deposit feeding or predatory ophiuroids dominated the megafaunal community in the northern Cape Basin, sponges, sipunculids and fish in the northern Angola Basin, and asteroids, crustaceans and fish in the eastern Guinea Basin, while in the western Guinea Basin sipunculids dominated.In the northern Cape Basin, peracarid crustaceans were the dominant macrofaunal group, followed by polychaetes and bivalves. In the Guinea Basin, polychaetes, peracarid crustaceans and bivalves dominated, although omnivorous or predatory free-living nematodes of macrofaunal size (>0.5 mm) made up 40–60% of the total abundance, with maxima in the western basin.The chlorophyll a content of sediments was lower in the northern Cape and Angola Basins than in the Guinea Basin, which was consistent with the differences in water masses, primary production and flux rate of organic matter in the three basins of the South-East Atlantic. The differences in structure and function of the macro- and megafauna communities in the three basins correlated with the differences in the amount of food reaching the seafloor in tropical and subtropical settings.     

Comparative performances of two- and three-dimensional analyses of soil-cement mixing columns under an embankment load

Abstract

This research presents measurements and simulations of the full-scale behavior of a test embankment built on a soft marine clay deposit improved using soil–cement mixing (SCM) columns in Bangkok, Thailand, using both two-dimensional (2D) and 3D finite element analyses (FEAs). Fixed SCM columns with two different installation patterns, that is, column groups and column rows, were constructed in the soft clay foundation prior to the construction of the embankment. Three column wall methods, namely, equivalent width, equivalent axial rigidity, and equivalent flexural rigidity approaches, were used to convert the 3D individual columns into 2D plane strain column walls. A comparison of the results obtained through the 3D and 2D FEAs revealed that the 2D analyses provide inaccurate results in terms of the column lateral movements, bending moments, and axial loads induced in the SCM columns in addition to the factors of safety against slope failure. This outcome occurred because the actual columns in the 2D FEA were modeled using extended walls, which essentially prevent the movements of soil between two columns or column rows. Correction factors used to convert the 2D analysis results into 3D analysis results were also proposed in this study.     

基于.NET反射技术的插件式GIS软件设计原理与实现

当前主流的GIS软件开发方式--组件式开发已难以适应日益复杂多变的GIS应用需求,尤其表现在GIS应用软件的扩展和维护方面.该文在分析当前流行的插件技术的基础上,给出在.NET 平台上开发插件式GIS应用软件的一种有效解决方案,运用该技术设计了一款插件式GIS软件:DotMap Desktop,通过整合一些开源GIS组件能够完成常见的GIS任务且具有良好的扩展性.采用该方案设计的插件式GIS软件能够方便地运行在各种主流的操作系统上.     

Crustal wide-angle reflection imaging along Lianxian-Gangkou profile in Guangdong province,China

A 400 km-long wide-angle seismic experiment along Lianxian-Gangkou profile in South China was carried out to study contact relationship between southeast continental margin of Yangtze block and northwest continental margin of Cathaysia block. We reconstructed crustal wide-angle reflection structure by the depth-domain pre-stack migration and the crustal velocity model constructed from the traveltime fitting. The wide-angle reflection section shows different reflection (from crystalline basement and Moho) pattern beneath the Yangtze and Cathaysia blocks, and suggests the Wuchuan-Sihui fault is the boundary between them. A cluster of well-developed reflections on Moho and in its underlying topmost mantle probably comes from alternative thin layers, which may be seismic signature of strong interaction between crust and mantle in the tectonic environment of lithosphere extension.     

Deriving depths of deep chlorophyll maximum and water inherent optical properties: A regional model

The Bohai Sea is a semi-enclosed inland sea with case-2 waters near the coast. A comprehensive set of optical data was collected during three cruises in June, August, and September 2005 in the Bohai Sea. The vertical profile measurements, such as chlorophyll concentration, water turbidity, downwelling irradiance, and diffuse attenuation coefficient, showed that the Bohai Sea was vertically stratified with a relative clear upper layer superimposed on a turbid lower layer. The upper layer was found to correspond to the euphotic zone and the deep chlorophyll maximum (DCM) occurs at the base of this layer. By tuning a semi-analytical model (24 and 25) for the Bohai Sea, we developed a method to derive water inherent optical properties and the depth of DCM from above-surface measurements. Assuming a ‘fake’ bottom in the stratified water, this new method retrieves the ‘fake’ bottom depth, which is highly correlated with the DCM depth. The average relative error between derived and measured values is 33.9% for phytoplankton absorption at 440 nm, 25.6% for colored detrital matter (detritus plus gelbstoff) absorption at 440 nm, and 24.2% for the DCM depth. This modified method can retrieve water inherent optical properties and monitor the depth of DCM in the Bohai Sea, and the method is also applicable to other stratified waters.     

Crustal velocity structures and their tectonic implications in different tectonic block regions of the Chinese mainland

In this paper,the typical velocity structures and average velocities of the crust in six different active tectonic block regions are presented on the basis of previous studies and their tectonic implications are discussed. The results show that different tectonic units have different features of crustal velocity structures. In general,there are low velocity distributions in the crust in regions with strong tectonic activities,and the scales of low velocity distributions are related to the tectonic activitie...     

宁化—大田—惠安地壳构造与速度结构特征

福建地处欧亚大陆东南缘,新构造活动强烈,区内北东向断裂带异常发育,是华南震区中、强地震活动的频发区.为深入认识我国东南沿海地壳上地幔速度结构特征及其深部构造背景,福建省地震局联合中国地震局地球物理勘探中心于2010年至2012年在福建陆域实施由18次人工爆破、四条北西向原生纵测线和四条北东向集成纵测线构成的三维人工地震测深实验.本文对该实验中以北西-南东走向近似垂直穿过政和—海丰断裂的宁化—大田—惠安深地震测深测线数据进行处理解释,采用地震射线走时正演构建了该剖面二维地壳速度模型.结果显示,沿剖面地壳厚度由西向东逐渐减薄,其西北侧地壳厚约31.8km,东南侧地壳厚达28.4km.剖面上地壳P波速度从5.90km·s~(-1)逐渐增加至6.20km·s~(-1),上地壳厚度横向变化不大,厚度在16~17km左右,但是下地壳厚度由西向东减薄较为明显.地壳以政和—海丰断裂为界,东西两段具有明显不同的速度结构,呈西段速度偏低、东段速度较高的特性,且西段在上下地壳分界面下方存在一个低速层.研究表明,剖面不同区段呈现出的速度结构差异与该区大地构造单元的划分基本吻合,剖面解释结果和以往远震接收函数研究结果均印证了作为闽西南坳陷带和闽东火山断陷带分界线的政和—海丰断裂是一条切割至下地壳底部的深大断裂.